The team compared the findings with responses to a web survey in which the same individuals were asked to indicate whether they preferred mornings or evenings.

The study, published in Nature Communications, reported a link between more than a dozen gene variants and healthy individuals who said they were at their best in the morning.

Early risers were significantly less likely to have insomnia or need more than eight hours of sleep per night. They were also less prone to depression than the 56% of respondents who described themselves as night owls.

The researchers also found that after taking into account the effect of age and sex, morning people were likely to have lower – and thus generally more healthy – BMI, or body-mass index, a measure of the ratio between height and weight.

None of these correlations, the researchers cautioned, necessarily implied a cause-and-effect relationship.

Nor did the team find genetic links with sleep disorders such as insomnia, apnoea or sweating while asleep.

The mechanism controlling circadian rhythms is found in neurons located in a part of the brain called the suprachiasmatic nuclei, in the hypothalamus.

The same process is involved in jetlag, which is the feeling of being out of phase – either sleepy or wide awake – with a given time cycle.